A plurality of different mechanisms is known from the prior art governing how data can be routed in communication networks with a plurality of network nodes along paths in the network. In publication WO 2008/058933 A1 a method is described for setting up bidirectional data transmission paths in a wireless meshed communication network with a plurality of network nodes. In this patent a routing tree is established starting from a node functioning as a root node between the wirelessly communicating network nodes, with the root node transmitting routing requests to the network nodes at regular intervals for creating the routing tree. Using the routing requests in this case a unidirectional data transmission path from the respective network nodes in the routing tree through to the root node is established first of all. By using two flags in the respective network node it can be achieved that under specific circumstances in response to a received routing request a routing reply is also sent back to the root node which causes a return path to be established from the root network node to the network node sending the routing reply. This enables a bidirectional data transmission path to be created between root network node and the network node sending the routing reply if necessary. In this publication it is not specified how a change between a mode in which bidirectional data paths are created and a mode in which only unidirectional data paths are created can be initiated by the root node.
In Standard IEEE 802.11s, which describes data transmission in the L2 layer in wireless meshed networks, the HWMP protocol (HWMP=Hybrid Wireless Mesh Protocol) for setting up data transmission paths is described. A routing tree is created with this protocol proactively with the aid of routing requests which are sent out from the corresponding root node in the routing tree. In this case a flag in the routing requests is used to specify whether in response to the receipt of a routing request in a network node a corresponding routing reply is to be sent out, i.e. whether a mode for establishing unidirectional or bidirectional data transmission paths is to be used. There is no description of how, by setting flags in the network node without explicit account taken of the mode in the routing reply, a switch can be made between the modes.